Abstract:

There is provided a communication apparatus including a reference
electrode; a signal electrode which electrostatically couples to a
communication medium a measurement unit for measuring an impedance of a
circuit system including between the reference electrode and the signal
electrode; and a transmission processing unit for creating a potential
difference between the signal electrode and the reference electrode based
on a transmission power corresponding to the impedance of the circuit
system measured by the measurement unit, and transmitting a signal to
another communication apparatus electrostatically coupled to the
communication medium.

Claims:

1. A communication apparatus comprising:a reference electrode;a signal
electrode which electrostatically couples to a communication medium;a
measurement unit for measuring an impedance of a circuit system including
between the reference electrode and the signal electrode; anda
transmission processing unit for creating a potential difference between
the signal electrode and the reference electrode based on a transmission
power corresponding to the impedance of the circuit system measured by
the measurement unit, and transmitting a signal to another communication
apparatus electrostatically coupled to the communication medium.

2. The communication apparatus according to claim 1, whereinthe
measurement unit includes a generation source of an AC signal to be
output to the circuit system for measurement of the impedance; andthe
transmission processing unit transmits the signal using the AC signal
output by the generation source as a carrier wave.

3. The communication apparatus according to claim 2, wherein the
measurement unit measures the impedance of the circuit system
simultaneously with the transmission of the signal by the transmission
processing unit using the AC signal.

4. The communication apparatus according to claims 1 to 3, wherein the
transmission processing unit transmits the signal based on a high
transmission power, the higher the impedance of the circuit system.

5. A communication apparatus comprising:a reference electrode;a signal
electrode which electrostatically couples to a communication medium;a
measurement unit for measuring an impedance of a circuit system including
between the reference electrode and the signal electrode; anda reception
processing unit for receiving a signal transmitted from another
communication apparatus electrostatically coupled to the communication
medium by detecting a potential difference between the signal electrode
and the reference electrode at a reception sensitivity corresponding to
the impedance of the circuit system measured by the measurement unit.

6. The communication apparatus according to claim 5, whereinthe
measurement unit includes a generation source of an AC signal to be
output to the circuit system for measurement of the impedance; andthe
reception processing unit demodulates the signal transmitted from another
communication apparatus using the AC signal output by the generation
source.

7. The communication apparatus according to claim 5 or 6, wherein the
reception processing unit receives the signal at a high reception
sensitivity, the higher the impedance of the circuit system.

8. A communication system comprising:a first communication apparatus
including,a first reference electrode,a first signal electrode which
electrostatically couples to a communication medium,a measurement unit
for measuring an impedance of a circuit system including between the
first reference electrode and the first signal electrode, anda
transmission processing unit for creating a potential difference between
the first signal electrode and the first reference electrode based on a
transmission power corresponding to the impedance of the circuit system
measured by the measurement unit and transmitting a signal to another
communication apparatus electrostatically coupled to the communication
medium; anda second communication apparatus including,a second reference
electrode,a second signal electrode which electrostatically couples to a
communication medium, anda reception processing unit for receiving a
signal transmitted from the first communication apparatus by detecting a
potential difference between the second signal electrode and the second
reference electrode.

9. A communication method comprising the steps of:measuring an impedance
of a circuit system including between a first reference electrode and a
first signal electrode electrostatically coupled to a communication
medium of a first communication apparatus;controlling a transmission
power of a signal according to the measured impedance of the circuit
system;transmitting the signal by creating a potential difference between
the first signal electrode and the first reference electrode based on the
controlled transmission power; andreceiving the signal transmitted from
the first communication apparatus by detecting a potential difference
between a second reference electrode and a second signal electrode
electrostatically coupled to the communication medium of the second
communication apparatus.

10. A communication apparatus comprising:a reference electrode;a signal
electrode which electrostatically couples to a communication medium;a
first oscillating unit for oscillating a first AC signal having a first
frequency;a second oscillating unit for oscillating a second AC signal
having a second frequency; anda modulation unit for generating a
modulation signal by switching and using the first AC signal or the
second AC signal, and outputting the modulation signal to the reference
electrode and the signal electrode.

11. A communication apparatus comprising:a reference electrode;a signal
electrode which electrostatically couples to a communication medium;a
first oscillating unit for oscillating a first AC signal having a first
frequency;a second oscillating unit for oscillating a second AC signal
having a second frequency; anda reception processing unit for receiving a
modulation signal transmitted from another communication apparatus
electrostatically coupled to the communication medium by detecting a
potential difference between the reference electrode and the signal
electrode, and demodulating the modulation signal using the first AC
signal or the second AC signal.

12. A communication system comprising:a first communication apparatus
including,a first reference electrode,a first signal electrode which
electrostatically couples to a communication medium,a first oscillating
unit for oscillating a first AC signal having a first frequency,a second
oscillating unit for oscillating a second AC signal having a second
frequency, anda modulation unit for generating a modulation signal by
switching and using the first AC signal or the second AC signal, and
outputting the modulation signal to the first reference electrode and the
first signal electrode; anda second communication apparatus including,a
second reference electrode,a second signal electrode which
electrostatically couples to a communication medium,a third oscillating
unit for oscillating the first AC signal having the first frequency,a
fourth oscillating unit for oscillating the second AC signal having the
second frequency, anda reception processing unit for receiving a
modulation signal transmitted from the first communication apparatus by
detecting a potential difference between the second reference electrode
and the second signal electrode, and demodulating the modulation signal
using the first AC signal or the second AC signal.

13. A communication method comprising the steps of:generating a first
modulation signal using a first AC signal, and transmitting the first
modulation signal from a first reference electrode and a first signal
electrode electrostatically coupled to a communication medium;generating
a second modulation signal using a second AC signal, and transmitting the
second modulation signal from the first reference electrode and the first
signal electrode;receiving the first modulation signal or the second
modulation signal by detecting a potential difference between a second
reference electrode and a second signal electrode electrostatically
coupled to the communication medium;modulation processing the first
modulation signal or the second modulation signal using the first AC
signal; andmodulation processing the first modulation signal or the
second modulation signal using the second AC signal.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a communication apparatus, a
communication system, and a communication method.

[0003]2. Description of the Related Art

[0004]Researches related to electrostatic field communication having human
body, space, and the like as a communication medium are being widely
carried out in recent years. For instance, the electrostatic field
communication is carried out between two communication apparatuses
including a reference electrode and a signal electrode. More
specifically, the signal electrodes of both communication apparatuses and
the human body electrostatically couple, and the reference electrodes of
both communication apparatuses and the space electrostatically couple to
form a closed circuit. The communication apparatus on a transmission side
transmits a signal by creating a potential difference between the signal
electrode and the reference electrode, and the communication apparatus on
the reception side receives the signal by detecting the potential
difference between the signal electrode and the reference electrode. Such
electrostatic field communication is described, for example, in Japanese
Patent Application Laid-Open No. 2006-324775 below.

SUMMARY OF THE INVENTION

[0005]However, if a human uses the communication apparatus by holding it
with his/her hand, the electrostatic coupling of not only the signal
electrode but also the reference electrode and the human body (hand) may
become strong depending on the way the communication apparatus is being
held. As a result, the potential difference created between the signal
electrode and the reference electrode lowers, and the communication
characteristics lower.

[0006]The present invention addresses the above-identified, and other
issues associated with methods in related art and apparatuses, and it is
desirable to provide a new and improved communication apparatus capable
of stabilizing the communication characteristics irrespective of the
positional relationship of the communication medium and the communication
apparatus, a communication system, and a communication method.

[0007]According to an embodiment of the present invention, there is
provided a communication apparatus including, a reference electrode, a
signal electrode which electrostatically couples to a communication
medium; a measurement unit for measuring an impedance of a circuit system
including between the reference electrode and the signal electrode, and a
transmission processing unit for creating a potential difference between
the signal electrode and the reference electrode based on a transmission
power corresponding to the impedance of the circuit system measured by
the measurement unit, and transmitting a signal to another communication
apparatus electrostatically coupled to the communication medium.

[0008]The measurement unit may include a generation source of an AC signal
to be output to the circuit system for measurement of the impedance, and
the transmission processing unit may transmit the signal using the AC
signal output by the generation source as a carrier wave.

[0009]The measurement unit may measure the impedance of the circuit system
simultaneously with the transmission of the signal by the transmission
processing unit using the AC signal.

[0010]The transmission processing unit may transmit the signal based on a
high transmission power, the higher the impedance of the circuit system.

[0011]According to another embodiment of the present invention, there is
provided a communication apparatus including, a reference electrode; a
signal electrode which electrostatically couples to a communication
medium; a measurement unit for measuring an impedance of a circuit system
including between the reference electrode and the signal electrode, and a
reception processing unit for receiving a signal transmitted from another
communication apparatus electrostatically coupled to the communication
medium by detecting a potential difference between the signal electrode
and the reference electrode at a reception sensitivity corresponding to
the impedance of the circuit system measured by the measurement unit.

[0012]The measurement unit may include a generation source of an AC signal
to be output to the circuit system for measurement of the impedance, and
the reception processing unit may demodulate the signal transmitted from
another communication apparatus using the AC signal output by the
generation source.

[0013]The reception processing unit may receive the signal at a high
reception sensitivity, the higher the impedance of the circuit system.

[0014]According to another embodiment of the present invention, there is
provided a communication system including, a first communication
apparatus including, a first reference electrode, a first signal
electrode which electrostatically couples to a communication medium, a
measurement unit for measuring an impedance of a circuit system including
between the first reference electrode and the first signal electrode, and
a transmission processing unit for creating a potential difference
between the first signal electrode and the first reference electrode
based on a transmission power corresponding to the impedance of the
circuit system measured by the measurement unlit and transmitting a
signal to another communication apparatus electrostatically coupled to
the communication medium, and a second communication apparatus including,
a second reference electrode, a second signal electrode which
electrostatically couples to a communication medium, and a reception
processing unit for receiving a signal transmitted from the first
communication apparatus by detecting a potential difference between the
second signal electrode and the second reference electrode.

[0015]According to another embodiment of the present invention, there is
provided a communication method including the steps of, measuring an
impedance of a circuit system including between a first reference
electrode and a first signal electrode electrostatically coupled to a
communication medium of a first communication apparatus, controlling a
transmission power of a signal according to the measured impedance of the
circuit system, transmitting the signal by creating a potential
difference between the first signal electrode and the first reference
electrode based on the controlled transmission power, and receiving the
signal transmitted from the first communication apparatus by detecting a
potential difference between a second reference electrode and a second
signal electrode electrostatically coupled to the communication medium of
the second communication apparatus.

[0016]According to another embodiment of the present invention, there is
provided a communication apparatus including, a reference electrode, a
signal electrode which electrostatically couples to a communication
medium, a first oscillating unit for oscillating a first AC signal having
a first frequency, a second oscillating unit for oscillating a second AC
signal having a second frequency, and a modulation unit for generating a
modulation signal by switching and using the first AC signal or the
second AC signal, and outputting the modulation signal to the reference
electrode and the signal electrode.

[0017]According to another embodiment of the present invention, there is
provided a communication apparatus including, a reference electrode, a
signal electrode which electrostatically couples to a communication
medium, a first oscillating unit for oscillating a first AC signal having
a first frequency, a second oscillating unit for oscillating a second AC
signal having a second frequency, and a reception processing unit for
receiving a modulation signal transmitted from another communication
apparatus electrostatically coupled to the communication medium by
detecting a potential difference between the reference electrode and the
signal electrode, and demodulating the modulation signal using the first
AC signal or the second AC signal.

[0018]According to another embodiment of the present invention, there is
provided a communication system including, a first communication
apparatus including, a first reference electrode, a first signal
electrode which electrostatically couples to a communication medium a
first oscillating unit for oscillating a first AC signal having a first
frequency, a second oscillating unit for oscillating a second AC signal
having a second frequency, and a modulation unit for generating a
modulation signal by switching and using the first AC signal or the
second AC signal, and outputting the modulation signal to the first
reference electrode and the first signal electrode, and a second
communication apparatus including, a second reference electrode, a second
signal electrode which electrostatically couples to a communication
medium, a third oscillating unit for oscillating the first AC signal
having the first frequency, a fourth oscillating unit for oscillating the
second AC signal having the second frequency, and a reception processing
unlit for receiving a modulation signal transmitted from the first
communication apparatus by detecting a potential difference between the
second reference electrode and the second signal electrode, and
demodulating the modulation signal using the first AC signal or the
second AC signal.

[0019]According to another embodiment of the present invention, there is
provided a communication method including the steps of, generating a
first modulation signal using a first AC signal, and transmitting the
first modulation signal from a first reference electrode and a first
signal electrode electrostatically coupled to a communication medium,
generating a second modulation signal using a second AC signal, and
transmitting the second modulation signal from the first reference
electrode and the first signal electrode, receiving the first modulation
signal or the second modulation signal by detecting a potential
difference between a second reference electrode and a second signal
electrode electrostatically coupled to the communication medium,
modulation processing the first modulation signal or the second
modulation signal using the first AC signal, and modulation processing
the first modulation signal or the second modulation signal using the
second AC signal.

[0020]According to the embodiments of the present invention described
above, the communication characteristics can be stabilized irrespective
of the positional relationship between the communication medium and the
communication apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is an explanatory view showing a configuration example of a
communication system according to the present embodiment;

[0022]FIG. 2 is an explanatory view showing a specific example of the
positional relationship of a communication apparatus and a communication
medium;

[0023]FIG. 3 is a function block diagram showing a configuration of a
communication apparatus according to a first embodiment of the present
invention;

[0024]FIG. 4 is an explanatory view showing a configuration example of an
impedance measurement unit.

[0025]FIG. 5 is an explanatory view showing a configuration of an
impedance measurement unit according to a variant;

[0026]FIG. 6 is a function block diagram showing a configuration of a
transmission processing unit;

[0027]FIG. 7 is a function block diagram showing the configuration of a
reception processing unit;

[0028]FIG. 8 is an explanatory view showing an example of the timing to
execute the transmission process the reception process, and the
measurement of the impedance;

[0029]FIG. 9 is an explanatory view showing a variant of the impedance
measurement unit and the transmission processing unit;

[0030]FIG. 10 is an explanatory view showing another example of the timing
to execute the transmission process, the reception process, and the
measurement of the impedance;

[0031]FIG. 11 is a sequence chart showing a flow of the communication
method executed in the communication apparatuses according to the first
embodiment;

[0032]FIG. 12 is an explanatory view showing a relationship of the
position of the communication medium and the electric field intensity;

[0033]FIG. 13 is an explanatory view showing a configuration example of a
transmission processing unit according to a second embodiment;

[0034]FIG. 14 is an explanatory view showing a configuration example of a
reception processing unit according to the second embodiment; and

[0035]FIG. 15 is an explanatory view showing a communication example
according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036]Hereinafter, preferred embodiments of the present invention will be
described in detail with reference to the appended drawings. Note that,
in this specification and the appended drawings, structural elements that
have substantially the same function and stricture are denoted with the
same reference numerals and repeated explanation of these structural
elements is omitted.

[0037]The DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS" will be
described according to the following order of items.

[0038](1) Outline of communication system according to present embodiment

[0039](2) Communication apparatus according to first embodiment of present
invention

[0040](3) Communication apparatus according to second embodiment of
present invention

[0041](4) Conclusion

[1] OUTLINE OF COMMUNICATION SYSTEM ACCORDING TO PRESENT EMBODIMENT

[0042]First, a communication system 1 according to the present embodiment
will be schematically described with reference to FIG. 1.

[0043]FIG. 1 is an explanatory view showing a configuration example of a
communication system 1 according to the present embodiment. As shown in
FIG. 1, the communication system 1 according to the present embodiment
includes a plurality of communication apparatuses 100A and 100B, and a
communication medium 20. The communication apparatuses 100A and 100B have
a function serving as a transmission side and a function serving as a
reception side, but a case where the communication apparatus TOGA
functions as the transmission side and the communication apparatus 100B
functions as the reception side will be described below. In FIG. 1, a
capital letter alphabet is given after the reference numeral such as the
communication apparatuses 100A and 100B to distinguish each
configuration, but the communication apparatus is simply termed as the
communication apparatus 100 and the like if each configuration does not
need to be particularly distinguished.

[0044]The communication apparatus 100A includes a signal electrode 110A, a
reference electrode 120A, and a signal processing unit 130A. The signal
electrode 110A is an electrode for forming electrostatic coupling with
the communication medium 20, and the reference electrode 120A is an
electrode for forming electrostatic coupling with the space. The signal
processing unit 130A has a function serving as a transmission processing
unit for transmitting a signal by creating a potential difference between
the signal electrode 110A and the reference electrode 120A. The signal
transmitted by the signal processing unit 130A includes a music signal of
music, lecture, radio program, and the like; an image signal of movies
television program, video program, photograph, document, picture, figure,
and the like; and an arbitrary signal of game, software, and the like.

[0045]The communication medium 20 is an object having dielectric property,
conductivity, or the like capable of transmitting electrical signals. In
this specification, human body is given as an example of the
communication medium 20, but the communication medium 20 is not limited
to a human body. For instance, the communication medium 20 may be an
arbitrary object including a metal which is a conductive material such as
aluminum, copper, iron, and alloy, a dielectric material such as plastic,
ceramic rubber, or glass, and a living body including plants and animals
having the properties of both the conductive material and the dielectric
material.

[0046]The communication apparatus 100B includes a signal electrode 110B, a
reference electrode 120B, and a signal processing unit 130B. The signal
electrode 110B is an electrode for forming electrostatic coupling with
the communication medium 20, and the reference electrode 120B is an
electrode for forming electrostatic coupling with the space. The signal
processing unit 130B has a function serving as a reception processing
unit for receiving a signal transmitted from the communication apparatus
100A by detecting the potential difference created between the signal
electrode 110B and the reference electrode 120B.

[0047]The influence of the positional relationship of the communication
apparatus 100A and the communication medium 20 on the communication
characteristics will be described with reference to FIG. 2

[0048]FIG. 2 is an explanatory view showing a specific example of the
positional relationship of the communication apparatus 100A and the
communication medium 20. In state 1 shown in FIG. 2, a space exists
between the signal electrode 110A and the communication medium 20, and
the signal electrode 110A and the communication medium 20 are not
electrically coupled, and thus electrostatic capacity forms between the
signal electrode 110A and the communication medium 20. The reference
electrode 120A is arranged with a distance from the signal electrode
110A, and the distance with the communication medium 20 is longer than
that of the signal electrode 110A, and thus the electrostatic coupling
with the communication medium 20 is sufficiently weaker than the signal
electrode 110A. Therefore, if only the signal electrode 110A is strongly
electrostatically coupled to the communication medium 20 as in the state
1 shown in FIG. 2, the signal transmitted from the signal electrode 110A
is efficiently transmitted to the communication apparatus 100B, and thus
the state 1 is considered as an ideal usage state.

[0049]In the communication apparatus 100B on the reception side as well,
in a state only the signal electrode 110B is strongly electrostatically
coupled to the communication medium 20, the potential difference created
between the signal electrode 110B and the reference electrode 120B by the
signal from the communication apparatus 100A becomes a high gaily, and
thus such state is considered as an ideal usage state.

[0050]When the user uses the communication apparatus 100A by holding it
with his/her hand, the communication medium 20 reaches the vicinity of
the reference electrode 120A, as shown in state 2 of FIG. 2, depending on
the way the communication apparatus 100A is being held. In this case, not
only the signal electrode 110A, but the electrostatic coupling of the
reference electrode 120A and the communication medium 20 also becomes
stronger. As a result, the potential difference level of the signal
electrode 110A and the reference electrode 120A lowers, and the
communication characteristics degrade.

[0051]In the communication apparatus 100B on the reception side as well,
when the electrostatic coupling of the reference electrode 1203 and the
communication medium 20 becomes stronger, the potential difference
created between the signal electrode 110B and the reference electrode
120B by the signal from the communication apparatus 100A becomes a low
gain.

[0052]The communication apparatuses 100A and 100B according to the first
embodiment of the present invention have been contrived focusing on the
above situation. According to the communication apparatuses 100A and 100B
of the first embodiment of the present invention, the communication
characteristics can be stabilized irrespective of the positional
relationship with the communication medium 20. The first embodiment of
the present invention will be described in detail with reference to FIGS.
3 to 11.

(2) COMMUNICATION APPARATUS ACCORDING TO FIRST EMBODIMENT OF PRESENT
INVENTION

[0053]FIG. 3 is a function block diagram showing a configuration of the
communication apparatus 100 according to the first embodiment of the
present invention. As shown in FIG. 3, the communication apparatus 100
includes a signal electrode 110, a reference electrode 120, and a signal
processing unit 130 including a transmission processing unit 140, a
reception processing unit 150 and an impedance measurement unit 160. The
specific configuration will be described below in the order of the
impedance measurement unit 160, the transmission processing unit 140, and
the reception processing unit 150.

[0054]FIG. 4 is an explanatory view showing a configuration example of the
impedance measurement unit 160. As shown in FIG. 4, the impedance
measurement unit 160 includes a resistor element Ri, a measurement unit
162 and an AC (Alternating Current) signal generating unit 164. FIG. 4
shows an equivalent circuit of a circuit system including between the
signal electrode 110 and the reference electrode 120. E1 in FIG. 4
corresponds to the signal electrode 110 and E2 corresponds to the
reference electrode 120.

[0055]In FIG. 4, an inductance L is a component parasitizing to the
circuit system. A capacitance C12 is an electrostatic capacity formed
between the signal electrode 110 and the reference electrode 120. A
capacitance C1b is an electrostatic capacity formed between the signal
electrode 110 and the communication medium 20. A capacitance C1g shows an
electrostatic capacity with respect to space of the signal electrode 110.

[0056]A capacitance C2b is an electrostatic capacity formed between the
reference electrode 120 and the communication medium 20. A capacitance
C2g shows an electrostatic capacity with respect to space of the
reference electrode 120.

[0057]A resistance Rb1 and a resistance Rb2 are resistance values of the
communication medium 20, and occur by the conductivity of the
communication medium 20. A capacitance Cbg shows an electrostatic
capacity with respect to space of the communication medium 20.

[0058]The AC signal generating unit 164 (generation source) of the
impedance measurement unit 160 generates a predetermined AC signal
(assume frequency near carrier wave), and outputs the generated AC signal
to the circuit system. The measurement unit 164 measures the signal of
both ends of the resistor element Ri. The amplitude and the phase
generated at the resistor element Ri by the AC signal output from the AC
signal generating unit 164 depend on the impedance of the circuit system.
Therefore, the measurement unit 162 can detect the impedance of the
circuit system based on the amplitude and the phase of the AC signal in
the resistor element Ri.

[0059]In state 2 shown in FIG. 2, the capacitance value of the C2b is
assumed to be lower than in state 1, and the impedance of the circuit
system including between the signal electrode 110 and the reference
electrode 120 is assumed to rise (transmission degree of signal lowers).
Therefore, in what state the positional relationship of the communication
apparatus 100 and the communication medium 20 is in can be understood
based on the impedance detected by the measurement unit 162.

[0060]FIG. 4 merely shows one example of the configuration of the
impedance measurement unit 160, and the present invention is not limited
to the configuration of the impedance measurement unit 160 shown in FIG.
4. For instance, the configuration of an impedance measurement unit 160'
shown in FIG. 5 is also applicable.

[0061]FIG. 5 is an explanatory view showing a configuration of the
impedance measurement unit 160' according to a variant. As shown in FIG.
5, the impedance measurement unit 160' according to the variant includes
a frequency measurement unit 166, and an AC signal generating unit 168.
Here, the AC signal generating unit 168 generates an AC signal of a
frequency dependent on the impedance of the circuit system, and outputs
the AC signal. In other words, in the variant, the circuit system forms a
Colpitts or Hartley oscillation circuit, and the AC signal generating
unit 168 generates the AC signal having an oscillating frequency of the
oscillation circuit. Therefore, the frequency measurement unit 166 can
detect the impedance of the circuit system by measuring the frequency of
the AC signal generated by the AC signal generating unit 168.

[0062]For instance, in the state 2 shown in FIG. 27 the capacitance value
of the C2b is assumed to be lower than the state 1, and the impedance of
the circuit system including between the signal electrode 110 and the
reference electrode 120 is assumed to rise (transmission degree of signal
lowers). Therefore, in what state the positional relationship of the
communication apparatus 100 and the communication medium 20 is in can be
understood based on the impedance detected by the measurement unit 166.

[0063]The configuration of the transmission processing unit 140 arranged
in the communication apparatus 100 according to the present embodiment
will be, described below with reference to FIG. 6.

[0065]The data signal generating unit 142 reads out data stored in an
arbitrary memory, processes the data as necessary, and outputs the data
as a data signal. In addition, the data signal generating unit 142 may
output communication control data (e.g., ACK), or transmission request
data of arbitrary data, instruction data to the communication apparatus
100B, and the like to the communication apparatus 100B.

[0067]The carrier wave generating unit 144 generates the carrier wave of
the data signal generated by the data signal generating unit 142. More
specifically, the carrier wave generating unit 144 generates the carrier
wave having the transmission power (amplitude) corresponding to the
measurement result of the impedance by the impedance measurement unit
160. The multiplier 146 modulates the data signal generated by the data
signal generating unit 142 by multiplying the carrier wave generated by
the carrier wave generating unit 144 thereto, and outputs the modulation
signal to the signal electrode 110 and the reference electrode 120.

[0068]For instance, the carrier wave generating unit 144 may generate the
carrier wave having a large transmission power as the transmission degree
of the signal is assumed to be low, the larger the impedance measured by
the impedance measurement unit 160. According to such configuration, the
communication characteristics can be maintained even if the positional
relationship of the communication apparatus 100 and the communication
medium 20 corresponds to state 2 shown in FIG. 2.

[0069]The carrier wave generating unit 144 may generate the carrier wave
having a first transmission power when the impedance measured by the
impedance measurement unit 160 is smaller than a predetermined value, and
generate the carrier wave having a second transmission power greater than
the first transmission power when the impedance is greater than the
predetermined value. According to such configuration, the communication
can be stabilized irrespective of the positional relationship of the
communication apparatus 100 and the communication medium 20 by
transmitting the signal at the first transmission power in state 1 shown
in FIG. 2 and at the second transmission power in state 2.

[0070]An example of adjusting the transmission power by causing the
carrier wave generating unit 144 to generate the carrier wave according
to the impedance measured by the impedance measurement unit 160 has been
described, but the present invention is not limited to such example. For
instance, the transmission power may be adjusted by controlling the gain
of the modulation signal output from the multiplier 146 according to the
impedance measured by the impedance measurement unit 160.

[0071]In the above description, an example in which the transmission
processing unit 140 modulates the data signal with the AM (Amplitude
Modulation) modulation method has been described, but the present
invention is not limited thereto. The transmission processing unit 140
may modulate the data signal with an arbitrary modulation method such as
FM modulation (Frequency Modulation). PM modulation (Phase Modulation),
and QAM modulation (Quadrature Amplitude Modulation).

[0072]The configuration of the reception processing unit 150 arranged in
the communication apparatus 100 according to the present embodiment will
be described below with reference to FIG. 7.

[0073]FIG. 7 is a function block diagram showing the configuration of the
reception processing unit 150. As shown in FIG. 7, the reception
processing unit 150 includes a reception sensitivity control unit 154, an
AMP 156, a carrier wave generating unit 157, and a multiplier 158.

[0074]The potential difference between the signal electrode 110 and the
reference electrode 120 is input to the reception processing unit 150 as
a modulation signal. The AMP 156 amplifies the modulation signal at the
dynamic gain based on the control by the reception sensitivity control
unit 154. Thereafter, the multiplier 158 demodulates the modulation
signal by multiplying the carrier wave generated by the carrier wave
generating unit 157 and the modulation signal, and outputs the
demodulation signal.

[0075]The reception sensitivity control unit 154 causes the AMP 156 to
amplify the modulation signal at the amplification factor (reception
sensitivity) corresponding to the measurement result of the impedance by
the impedance measurement unit 160. For instance, the reception
sensitivity control unit 154 may enhance the amplification factor of the
modulation signal in the AMP 156 as the transmission degree of the signal
is assumed to be lower, the larger the impedance measured by the
impedance measurement unit 1660. According to such configuration, the
communication characteristics can be maintained even if the positional
relationship of the communication apparatus 100 and the communication
medium 20 corresponds to the state 2 shown in FIG. 2.

[0076]The reception sensitivity control unit 154 may cause the AMP 156 to
amplify the modulation signal at a first amplification factor when the
impedance measured by the impedance measurement unit 160 is smaller than
a predetermined value, and to amplify the modulation signal at a second
amplification factor when the impedance is greater than the predetermined
value. According to such configuration, the communication can be
stabilized irrespective of the positional relationship of the
communication apparatus 100 and the communication medium 20 by amplifying
the modulation signal at the first amplification factor in state 1 shown
in FIG. 2 and at the second amplification factor in state 2.

[0077]Subsequently, an example of the timing to execute the transmission
process, reception process, and measurement of the impedance will be
described with reference to FIG. 5.

[0078]FIG. 8 is an explanatory view showing an example of the timing to
execute the transmission process the reception process, and the
measurement of the impedance. As shown in FIG. 8, the impedance
measurement unit 160 can perform the measurement of the impedance in the
vacant time of the transmission process and the reception process, and
the transmission processing unit 140 and the reception processing unit
150 can perform the signal processing based on the measurement result of
the impedance.

[0079]An example of performing the measurement of the impedance
simultaneously with the transmission process will be described with
reference to FIGS. 9 and 10.

[0080]FIG. 9 is an explanatory view showing a variant of the impedance
measurement unit 160 and the transmission processing unit 140. In this
variant, the measurement unit 162 measures the amplitude and the phase in
the resistor element Ri of the modulation signal output from the
multiplier 146 to measure the impedance of the circuit system including
the signal electrode 110 and the reference electrode 120. The carrier
wave generating unit 144 generates the carrier wave having the
transmission power corresponding to the impedance measured by the
impedance measurement unit 160, and outputs the carrier wave to the
multiplier 146. The timing of executing the transmission process, the
reception process, and the measurement of the impedance in the variant is
shown in FIG. 10.

[0081]FIG. 10 is an explanatory view showing another example of the timing
to execute the transmission process, the reception process, and the
measurement of the impedance. As shown in FIG. 10, according to the
variant, the impedance can be measured at the same time as the
transmission process, and thus the throughput can be expected to enhance.
Furthermore the circuit scale and the cost can be saved since an
independent AC signal generating function may not be provided to measure
the impedance. Moreover, the reception processing unit 150 performs the
demodulation process using the carrier wave generated in the transmission
processing unit 140, whereby the circuit scale and the cost can be
further reduced.

[0082]The communication method executed in the communication apparatuses
100A and 110B according to the first embodiment of the present invention
described above will be briefly summarized with reference to FIG. 11.
FIG. 11 is a sequence chart showing a flow of the communication method
executed in the communication apparatuses 100A and 100B according to the
first embodiment. As shown in FIG. 11, the impedance measurement unit
160A of the communication apparatus 100A first measures the impedance of
the circuit system including between the signal electrode 110A and the
reference electrode 120A (S204). Similarly, the impedance measurement
unit 160B of the communication apparatus 100B measures the impedance of
the circuit system including between the signal electrode 110B and the
reference electrode 120B (S208).

[0083]Thereafter, the transmission control unit 140A of the communication
apparatus 100A controls the transmission power based on the impedance
measured by the impedance measurement unit 160A (S212). Similarly, the
reception control unit 150B of the communication apparatus 100B controls
the reception sensitivity based on the impedance measured by the
impedance measurement unit 160B (S216).

[0084]Subsequently, the transmission processing unit 140A, of the
communication apparatus 100A transmits the modulation signal at the
transmission power controlled in S212 (S220), and the reception
processing unit 150 of the communication apparatus 100B amplifies the
modulation signal at the reception sensitivity controlled in S216 and
demodulates the signal (S224).

(3) COMMUNICATION APPARATUS ACCORDING TO SECOND EMBODIMENT OF PRESENT
INVENTION

[0085]The communication apparatus 100 according to the first embodiment of
the present invention has been described with reference to FIGS. 3 to 11.
The communication apparatus 100 according to the second embodiment of the
present invention will now be described with reference to FIGS. 12 to 15.

[0086]FIG. 12 is an explanatory view showing a relationship of the
position of the communication medium 20 and the electric field intensity.
In FIG. 12, f1 shows the distribution of the electric field intensity of
when the signal is transmitted by the electric field at frequency f1 from
the signal electrode 110A, and f2 shows the distribution of the electric
field intensity of when the signal is transmitted by the electric field
at frequency f2 from the signal electrode 110A. Thus, the distribution of
the electric field intensity at the surface layer of the communication
medium 20 is assumed to be in a standing wave state as the communication
medium 20 has a specific physical size.

[0087]As a result, the communication apparatus 100B existing at position
P1 can receive the signal at sufficient intensity when the communication
apparatus 100A transmits the signal at the frequency f1, but the
reception intensity of the signal becomes weak when the communication
apparatus 100A transmits the signal at the frequency f2. If the
positional relationship of the communication apparatus 100A and the
communication apparatus 100B is known, the signal can be transmitted
using the frequency corresponding to the positional relationship, but the
positional relationship of the communication apparatus 100A and the
communication apparatus 100B often changes fluidly.

[0088]The second embodiment of the present invention is contrived focusing
on the above situation. According to the second embodiment of the present
invention, the communication quality can be guaranteed irrespective of
the position of the pair of communication apparatuses. The second
embodiment will be specifically described below.

[0089]FIG. 13 is an explanatory view showing a configuration example of a
transmission processing unit 140' according to the second embodiment. As
shown in FIG. 13, the transmission processing unit 140' according to the
second embodiment includes an oscillator OSC1 for oscillating the
frequency f1, an oscillator OSC2 for oscillating the frequency f2, and a
switching unit 148 in addition to the data signal generating unit 142 and
the multiplier 146.

[0090]The switching unit 148 outputs the carrier wave of the frequency f1
generated by the oscillator OSC1 (first oscillating unit) and the carrier
wave of the frequency f2 generated by the oscillator OSC2 (second
oscillating unit) alternately to the multiplier 146 in units of one frame
of the transmission data according to the communication method. The
multiplier 146 modulates the data signal (baseband signal) generated by
the data signal generating unit 142 by multiplying the carrier wave of
the alternately switched frequency f1 or frequency f2 thereto, and the
modulation signal is transmitted from the signal electrode 110A and the
reference electrode 120A.

[0091]FIG. 14 is an explanatory view showing a configuration example of a
reception processing unit 150' according to the second embodiment. As
shown in FIG. 14, the reception processing unit 150' according to the
second embodiment includes a multiplier 158A, a multiplier 158B, an
oscillator OSC1 for oscillating the frequency f1, and an oscillator OSC2
for oscillating the frequency f2.

[0092]The multiplier 158A multiples the carrier wave of the frequency f1
generated by the oscillator OSC1 (third oscillating unit), and the
modulation signal detected as the potential difference of the signal
electrode 110A and the reference electrode 120A. Similarly, the
multiplier 158B multiples the carrier wave of the frequency f2 generated
by the oscillator OSC2 (fourth oscillating unit), and the modulation
signal detected as the potential difference of the signal electrode 110A
and the reference electrode 120A. Therefore, the reception processing
unit 150' according to the second embodiment can enhance the reception
probability of at least one of the modulation signals transmitted by the
carrier wave of the frequency f1 or the frequency 2, as shown in FIG. 15.

[0093]FIG. 15 is an explanatory view showing a communication example
according to the second embodiment of the present invention. In the
example shown in FIG. 15, an example where the communication apparatus
100B fails in receiving the modulation signal transmitted from the
communication apparatus 100A at the carrier wave of the frequency f1 due
to the influence of the standing wave, but succeeds in receiving the
modulation signal transmitted at the carrier wave of the frequency f2 is
shown.

[0094]According to the present embodiment, even if the positional
relationship of the pair of communication apparatuses is unknown, the
reliability of the communication can be enhanced by multiply transmitting
the signal at different carrier waves.

[0095]The communication apparatus 100B that succeeded in the reception of
the signal transmitted by one carrier wave may return the ACK containing
the information indicating the carrier wave to the communication
apparatus 100A. The communication apparatus 100A may transmit the signal
using the carrier wave indicated by the information contained in the ACK
over a predetermined period. According to such configuration, the
communication apparatus 100A suppresses a case of transmitting the signal
using the carrier wave that may not be received by the communication
apparatus 100B, thereby enhancing the throughput.

[0096]If the reception of the signal from the communication apparatus 100A
is interrupted, the communication apparatus 100B may notify such fact to
the communication apparatus 100A. The communication apparatus 100A then
switches the carrier wave to use, and transmits the signal using the
carrier wave having a high possibility of reaching the communication
apparatus 100B.

[0097]If at which timing the signal using one of the carrier waves is
transmitted can be grasped in advance, the communication apparatus 100A
may not necessarily include a plurality of multipliers 158A and 158B as
shown in FIG. 14. In this case, the effects similar to above can be
expected by switching the carrier wave input to one multiplier based on
the timing gasped in advance.

(4) CONCLUSION

[0098]As described above, the communication apparatus 100 according to the
first embodiment of the present invention controls the transmission power
or the reception sensitivity according to the impedance between the
signal electrode 110 and the reference electrode 120. As a result, a
stable communication can be maintained irrespective of the strength of
the electrostatic coupling of the reference electrode 120 and the
communication medium 20.

[0099]The communication apparatus 100 according to the second embodiment
of the present invention transmits or receives the signal by multiply
using the carrier waves having different frequencies. Therefore, the
reception probability of the signal transmitted using one of the carrier
waves can be enhanced even if the signal transmitted to the communication
medium 20 is in the standing wave state.

[0100]It should be understood by those skilled in the art that various
modifications, combinations, sub-combinations and alterations may occur
depending on design requirements and other factors insofar as they are
within the scope of the appended claims or the equivalents thereof.

[0101]For instance, each step in the process of the communication
apparatuses 100A and 100B of the present specification may not
necessarily be processed in time-series along the order described as a
sequence chart. Each step in the process of the communication apparatuses
100A and 100B may include the process executed in parallel or
individually (e.g., parallel process or process by object).

[0102]The present application contains subject matter related to that
disclosed in Japanese Priority Patent Application JP 2008-150910 filed in
the Japan Patent Office on Jun. 9, 2008, the entire content of which is
hereby incorporated by reference.